Copolyimide membranes with high permeability and selectivity for olefin/paraffin separations

Abstract

A copolyimide polymer membrane is provided for separation of hydrocarbons including separation of olefins from paraffins and isoparaffins from other paraffins. The copolyimide polymer membranes include a poly(3,3′-diaminobenzophenone-3,3′,5,5′-tetramethyl-4,4′-methylene dianiline-pyromellitic dianhydride) (abbreviated as poly(DAB-TMMDA-PMDA)). The copolyimide membranes prepared from poly(DAB-TMMDA-PMDA) with varying molar ratios of DAB to TMMDA (abbreviated as PI-DAB-T) showed excellent separation properties for propylene/propane separation.

The invention claimed is: 
     
       1. A copolyimide membrane for olefin/paraffin separations comprising a copolyimide membrane that comprises a plurality of repeating units of formula (I) 
       
         
           
           
               
               
           
         
         wherein m and n are independent integers from 10 to 500; n/m is in a ratio from 10:1 to 1:10; Y1 is selected from the group consisting of 
       
       
         
           
           
               
               
           
         
         and mixtures thereof, wherein said copolyimide membrane comprises a poly(2,2′-bis(3-amino-4-hydroxyphenyl) hexafluoropropane-(3,3′,5,5′-tetramethyl-4,4′-methylene dianiline-pyromellitic dianhydride) or a poly(2,2′-bis(3-amino-4-methylphenyl) hexafluoropropane-(3,3′,5,5′-tetramethyl-4,4′-methylene dianiline-pyromellitic dianhydride). 
       
     
     
       2. The copolyimide membrane of  claim 1  fabricated into a form selected from the group consisting of hollow fibers, tubes, and flat sheets.